During certain engine operating conditions it is desirable to inject fuel using a split injection technique in which a portion of the total fuel to be delivered to the engine cylinder is injected by what is commonly termed a pilot shot or prime shot and in which the remaining portion of the fuel is injected by what is commonly termed a main shot. For example, it is known to utilize such a split injection technique at engine operating conditions including low engine speed and low engine load. In the past the controllability of such split injection has been somewhat restricted by mechanical limitations of the hydraulically-actuated injectors utilized. For example, some injectors have been limited in that the pilot or prime shot was mechanically controlled and therefore both a pilot shot and a main shot always occurred. Even with a more advanced hydraulically-actuated electronically-controlled injector, during certain engine operating conditions the quantity of fuel desired to be delivered to the engine can be relatively small. It is sometimes difficult to accurately control delivery of such small amounts of fuel, even utilizing current control signals.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.